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View Full Version : black spots and transperacy issues



dogbite
07-13-2006, 05:08 AM
1.i get black spots when i use a bump map, it happens because of the mipmap quality option in the image map.
if i use it on high the image doesnt work and if i use it in general i sometimes get black spots on the render.
it doesnt happen when i turn it off.

2.if my raytrace reflection level is set to below 7 or 10 i get some transperacy polygons that , to put it simply make everything in their path dissapear.
for example, if i have polygon hair with trans, some polygons look like there isnt a head behind them and show the background in the transperacy.

Dave Jerrard
07-16-2006, 10:29 PM
I can't really comment on the black spots without seeing them & where they're showing up, or what kinds of images you're using using mip-mapping on, but I can help out on the second point:

Lowering the Ray Recursion level will affect image quality. It's basially the number of surfaces a ray will see before ignoring everything and heading off to infinity, where it will see the backdrop color. If you set it to 2, a ray will only see two surfaces, maximum. If it's going through two windows (single sided, no air polygons), it will use up both recursions and will not see enything else through those two windows. In the case of your hair example, the rays are being told to give up tracing anything else after they've already passed through 7-10 layers of hair polygons. At that point, they just dump the backdrop color into the image and LW moves on to the next pixel.

Ray Recursion is not a speed control. Yes, it can make some scenes render faster, but it's at the cost of image quality. It's faster because it's doing less rendering of ray traced transparency (and refraction) and reflections. On scenes where a ray is likely to bounce between reflective or refractive surfaces repeatedly, turning this setting down will speed things up because it limits how many times that a ray will bounce like this. Fewer recursions = fewer ray trace calculations = less time. This also means you see through fewer transparent surfaces, and you see fewer reflections of reflections, etc.. When you go too low, those missing calculations can have a very noticeable effect on the image, as you found out.

Try bumping the recursion level up again, or just don't use transparency on the hair - try translucency instead.

He Who Has Done A Lot Of Refraction Tests In 3D.